Why is sed not recognizing \t as a tab?

Question

sed \"s/\\(.*\\)/\\t\\1/\" $filename > $sedTmpFile && mv $sedTmpFile $filename

I am expecting this sed script to insert a <

Answer 1

I've used something like this with a Bash shell on Ubuntu 12.04 (LTS):

To append a new line with tab,second when first is matched:

sed -i '/first/a \\t second' filename

To replace first with tab,second:

sed -i 's/first/\\t second/g' filename